A 34-year-old Texas man shot and killed 12 people at the Washington Navy Yard in Washington, D.C. on Monday. Authorities have confirmed 13 fatalities, including one shooter, identified by the Federal Bureau of Information as Aaron Alexis.

Alexis was a former full-time Navy reservist based in Texas when he left the reserves in 2011, according to the Associated Press. A law enforcement official told the AP that Alexis is believed to have gotten into the Navy Yard by using someone else’s identification card. It isn’t clear if that individual was an accomplice or if that person’s ID card was stolen.

As of Monday evening, more details about Alexis’ life are beginning to emerge. The Fort Worth Star-Telegram uploaded a video showing two of the paper’s editors recalling an exchange with Alexis to YouTube, while the Seattle Police Department wrote in a blog post that Alexis had been arrested in Seattle in 2004 for shooting the tires of another man’s vehicle:

Aaron Alexis, the man identified by Washington D.C. police as a suspect in this morning’s tragic attack on a US Navy Yard, was previously arrested by Seattle police in 2004 for shooting out the tires of another man’s vehicle in what Alexis later described to detectives as an anger-fueled “blackout.”

Because Seattle police have received numerous inquiries about the incident, we are posting the details, detective logs, and the original report for the May 6, 2004 case.

Officials are also looking into the possibility that another shooter could be at large. The status of one potential suspect, described as a black male around 50 years old wearing a military-style uniform and who may have been in possession of a long gun, remains unknown as of early Monday evening, according to D.C. Police Chief Cathy Lanier. The D.C. Police Department tweeted Monday that a man wearing a tan military outfit they earlier described as a potential suspect or person of interest was cleared of involvement in the shooting.

President Obama made a statement on the situation from the White House, calling the shootings “a cowardly act” and saying that the shooter or shooters will be held responsible.”Today we are confronting yet another mass shooting, and today it happened on a military installation in our nation’s capital,” the president said. “These are men and women who were going to work, doing their job protecting all of us. They’re patriots, and they know the dangers of serving abroad, but today they faced the unimaginable violence that they wouldn’t have expected here at home.”

Obama later ordered flags to be flown at half-staff until Friday, Sept. 20 in honor of the Navy Yard victims. The White House also indefinitely postponed an event celebrating latin music “in light of today’s tragic events.”

“We send our thoughts and prayers to all at the Navy Yard who have been touched by this tragedy,” Obama said. “We thank them for their service. We stand with the families of those who’ve been harmed.”

MedStar Washington Hospital Center confirms they’ve received three victims from the scene of the shooting. Chief Medical Officer Janis Orlowski said in a press conference that the hospital is treating one Metropolitan Police officer and two civilians. All are in critical condition but their “chances for survival very good.” All were able to talk, she said, but none gave specific details about what happened. Orlowski speculated that the weapon used “had to be a semi-automatic, because all victims described rapid succession gunshots.”

According to USA Today, Police described the first shooter as a black male, between 5’10 and 6 feet tall, wearing a black shirt and a black hat. Witnesses told the AP that a gunman opened fire from the fourth floor, aiming down on people in the first-floor cafeteria. Others said a gunman fired at them in a third-floor hallway, but it wasn’t clear whether the witnesses were describing the same gunman.

All flights were grounded temporarily at Washington’s Reagan National Airport earlier this morning due to the security risk, but departures resumed just after 10 a.m. The FAA has now lifted the ground stop and is resuming normal operations.

Senate officials told the AP the building will be shut down while another potential shooter is sought. Eight public schools and one private school in D.C. are also on lockdown as a precaution. Monday’s Washington Nationals game against the Atlanta Braves has been canceled.

“I’m deeply shocked and saddened by the shooting this morning at the Navy Yard,” said Secretary of the Navy Ray Mabus. “Our thoughts and prayers are with the victims and their families. I have complete confidence in our first responders, and I continue to be completely focused on this very difficult situation.”

The shooting was reported at the building at 8:20 a.m. ET. Personnel have been told to “shelter in place.” The building houses 3,000 service members, civilians and contractors who work on the Navy’s fleet and is the largest of the Navy’s five systems commands. A source across the street from Navy Yard tells TIME that authorities are “warning us to stay away from the windows. A couple Marines behind a vehicle [are] pointing guns in a direction away” from the building where the shooting was first reported. There’s “tons of activity facing another building about 100 yards east” of the Naval Sea Systems Command building, a source inside the Navy Yard confirms to TIME.

D.C. Horror: Shooting at Navy Yard

Jonathan Ernst / Reuters

A family member of a Navy Yard worker who was evacuated during a shooting arrives hoping to find him at a makeshift shelter at the Nationals Park baseball stadium near the naval installation in Washington, Sept. 16, 2013.

We don't
know ANYTHING of real substantiation here. The media AND the President
have used this tragedy to further political capital. Before jumping to
ANY conclusions we, the public, have to really know what happened. IF
this was a "long nut-case" then we have a duty to find what sets people
off to this extreme. If it's something else (TERROR) then the object
used have little to no relevance as a bomb can do much more damage than a
firearm.

The NRA told me the only thing that's able to stop a bad guy with a gun is a good guy with a gun. Were there no "good guys" present at this naval base? You know, if this keeps up it might challenge my poorly informed belief that somehow having MORE guns is keeping us safer. Especially those you can legally hide as this responsible gun owner did.

Job well done NRA. And now you've even gotten several states to load up even more guns into our nations schools. Last year conservatives spent the election complaining about all those overpaid teachers, calling them unionized thugs. This year they spend your tax dollars making sure those unionized thugs are ARMED TO THE TEETH. You can't trust them to negotiate their paycheck, but apparently you can trust them to use loaded, deadly weapons around your children.

And to think all this happens right after recalling two lawmakers in Colorado who had the gall to actually institute universal background checks... you know, something more than 90% of American's and even more than 70% of NRA members support. Absolutely brilliant, especially at a time in America when bullets are in such high demand that we can't even keep them on store shelves... all going to all of these responsible gun owners no doubt.

@OldTimerTwiceHisAge Military bases are generally gun-free zones except for the security. They are considerably better secured than schools, which are entirely defenseless, but only on-duty law enforcement and military security are actually armed on base.